Various positioning and navigation systems and methods are known, in which a platform of an unknown location (e.g. airborne platform, naval platform or a ground vehicle) communicates with a positioning system and is provided with information about its position relative to the positioning system (referred to as radial). A VHF Omnidirectional Range (VOR) system is a line-of-sight radio navigation system in which a ground station broadcasts an aircraft a VHF radio signal encoded with the angle to it, indicating the direction the aircraft lies from the station. Many VOR systems have another navigation aid called Distance Measuring Equipment (DME) at the same location, for providing the aircraft with its slant distance from the station. By knowing both the distance and radial from the station, the aircraft's position can be determined (“VHF omnidirectional range”, Wikipedia, http://en.wikipedia.org/wiki/VHF_omnidirectional_range).
The GPS (Global Positioning System) is another positioning and navigation system allowing a platform equipped with a GPS receiver (and one antenna) to be provided with information about its position relative to one or more GPS satellites orbiting the earth. As known, the precision of the GPS is typically in the range of 2-3 meters (before the year 2000 the precision of the signal available for non military users was even more limited). This imposes a drawback for devices and operations which require a better precision. Furthermore, the operation of the GPS satellite communication infrastructure is controlled by the US Government, which reserves the light to limit the signal strength or accuracy of the GPS system, or to shut it down completely. Additionally, the GPS signal can be blocked or jammed, e.g. by a transmitter radiating a relatively low power radiation in the vicinity of the GPS receiver. Additionally, the typical update rate of GPS data is in the range of 50-100 Hz. This rate is not sufficient for highly maneuvering platforms, such as missiles and certain airplanes.
U.S. Pat. No. 3,981,015 discloses a phase comparison radio navigation system in which a prime transmitting station and one or more secondary transmitting stations radiate phase-locked signals of the same frequency in a time-shared sequence. Phase locking at the secondary station or stations is effected by using a common phase comparator both for locking a phase memory oscillator to the receiving prime signals and for locking the secondary signals at the antenna with the phase memory oscillator.
U.S. Pat. No. 4,975,710 discloses methods, algorithms and apparatus for direction-of arrival (DOA) measurement/computation based on long-baseline, phase-difference, paired-antenna interferometry and on DOA-computing array processing algorithms. Specifically, methods and algorithms based on direct, cyclically unambiguous estimation of the cosine of the DOA are described for resolving the cyclic ambiguities in long-baseline, phase-difference paired-antenna interferometers, and for steeling the computations to the vicinities of the solutions in computation-intensive array processing algorithms, thereby reducing computation load and time.
U.S. Pat. No. 4,197,542 discloses an electronic navigation system ground station, which may be either an omni-range beacon (such as VOR) or a passive direction finder. A circular array of antenna elements has a feed arrangement which includes switched programming of at least one discrete set of phase shifters to effect successively changed phase-rotation fields for minimizing the adverse effects of multipath signals between the ground station and a remote station, aboard an aircraft for example.
U.S. Pat. Nos. 6,573,865 and 5,084,709 disclose multi-element antenna clusters or arrays for the reception and transmission of radio waves for direction-finding, navigation aid and emitter and/or receiver location purposes. In particular, they relate to arrangements of multiple antennas whereby the direction of propagation (arrival or departure) of a wavefront is determined from a combination of the amplitudes of phasor (or total individual antenna output) differences between pairs of antennas, said arrangements being along certain geometrical patterns, such as a circle, an ellipse, a polygon, an open straight line, etc., with at least one longest dimension measuring more than one wavelength of the incident or departing wave.
U.S. Pat. No. 3,967,277 discloses a radio navigation system which includes a first pair of fixed transmitting stations, a second pair of fixed transmitting stations and a mobile station. The mobile station includes a receiver having first means for deriving a first signal indicative of the difference in the distances between the mobile station and each of the first pair of fixed stations and second means for deriving a second signal indicative of the difference in the distances between the mobile station and each of the second pair of fixed stations. Summing means are provided for adding the first and second signals to obtain a third signal indicative of a first line of position on which the mobile station is located, and difference means are provided for subtracting one of the first and second signals from the other to obtain a fourth signal indicative of a second line of position on which the mobile station is located.
Therefore, there is a need in the art for a positioning system and method that allows a platform equipped with only one receiver and one antenna to be provided with highly accurate positioning information. There is a further need in the art for a positioning system and method which provides its operators with full control over the system. There is also a need in the art for a positioning system and method which cannot be easily jammed. There is a further need in the art for a positioning system providing update rate of more than 50-100 Hz. There is also a need in the art for a positioning system capable of operating in outer space.